I know it's specified as "dimension", but the problem is what to specify after dimension. I've tried "overworld", "region", and not specifying a dimension at all. At least one of them ought to work, but no.

I can look into a nether map as well, but they always end up looking horrible.

Feed the Beast is a different launcher entirely. I just plugged mine into a Feed the Beast folder in my Games/Minecraft folder. It keeps a separate, modded Minecraft jar (currently 1.5.2), along with all the resources.

There is currently a Creative Mode test server running on elyon.net, which will probably also be the address of the real server.